1. Field of the Invention
The present invention relates to a vertical-axis low head water turbine of the Kaplan type.
2. History of the Related Art
In cases where turbines ae operated at low head, i.e. where the heights or depth of fluid supply is measured between some meters and some tens of meters, vertical-axis Kaplan water turbines are used which are supplied via a water chamber, i.e. a feeding channel in the open air or under load. A truncated distributor converging downstream, i.e. downwardly in this case, is also conventionally used.
However, tests on reduced models of such turbines have demonstrated disturbing phenomena:
For example, in a water chamber, there are zones of dead water which promote the development of the eddies appearing at other points of the water chamber, but these dead water zones may themselves also give rise to the creation of vortices.
In addition, downstream of the shaft of said turbine or its circular sleeve, a separation of the flow of water is produced with appearance or creation of vortices. These vortices increase, taking along air beneath the free surface so that the vortices are transformed into suction eddies.